In this paper, a dynamic model of a rotor-ball bearing system is developed in Msc. ADAMS commercial software. Contacts between the balls and the rings are modelled according to Hertzian theory. The bearing model is capable of representing the effects of bearing defects and internal clearances. When they are coupled with the rotor structures, bearings without any defect can also cause excessive vibrations due to the resonance characteristics of the system. In order to demonstrate these characteristics the rotor itself is modelled as a flexible shaft and a disc positioned at the free end of the shaft. The rotor-ball bearing model developed here is capable of representing the gyroscopic effects and the behaviour of the system under different unbalance conditions. Various case studies are performed and Campbell diagrams are obtained by using short-time Fourier transform method.